[CGCilk] Fix cilk_for-loop code generation when emission of loop

variable may introduce new basic blocks.  Addresses issue llvm#77.

clang/lib/CodeGen/CGCilk.cpp

@@ -820,7 +820,7 @@ void CodeGenFunction::EmitCilkForStmt(const CilkForStmt &S,
     // detach.
     if (InvokeDest) {
       CGBuilderTy::InsertPoint SavedIP = Builder.saveIP();
-      Builder.SetInsertPoint(DetachBlock);
+      Builder.SetInsertPoint(Detach);
       // Create the new detach instruction.
       llvm::DetachInst *NewDetach = Builder.CreateDetach(
           ForBodyEntry, Continue.getBlock(), InvokeDest,

clang/test/Cilk/cilkfor-detach-unwind-rewrite.cpp

@@ -0,0 +1,50 @@
+// Check that detaches with unwind destinations are properly inserted
+// during CodeGen.
+//
+// RUN: %clang_cc1 %s -fopencilk -fsanitize=signed-integer-overflow,unsigned-integer-overflow -fcxx-exceptions -fexceptions -emit-llvm -fsanitize-recover=signed-integer-overflow,unsigned-integer-overflow -disable-llvm-passes -o - | FileCheck %s
+
+unsigned __cilkrts_get_nworkers(void);
+
+template <class T> class Reducer_sum {
+public:
+  Reducer_sum(long num_workers);
+  ~Reducer_sum();
+  void add(T new_value);
+  T get() const;
+};
+
+int main() {
+  Reducer_sum<long> total_red(__cilkrts_get_nworkers());
+  _Cilk_for(long i = 0; i < 100; i++) { total_red.add(5); }
+  return total_red.get();
+}
+
+// CHECK: define {{.*}}i32 @main()
+// CHECK: br i1 %{{.*}}, label %[[PFOR_PH:.+]], label %[[PFOR_END:[a-z0-9._]+]]
+
+// CHECK: [[PFOR_PH]]:
+// CHECK: call void @__ubsan_handle_sub_overflow
+// CHECK: call void @__ubsan_handle_sub_overflow
+// CHECK: call void @__ubsan_handle_divrem_overflow
+// CHECK: call void @__ubsan_handle_add_overflow
+
+// Check contents of the detach block
+// CHECK: load i64, i64* %[[INIT:.+]]
+// CHECK: load i64, i64* %[[BEGIN:.+]]
+// CHECK: call { i64, i1 } @llvm.smul.with.overflow.i64(
+// CHECK: br i1 %{{.*}}, label %[[CONT5:.+]], label %[[HANDLE_MUL_OVERFLOW:[a-z0-9._]+]],
+
+// CHECK: [[HANDLE_MUL_OVERFLOW]]:
+// CHECK: call void @__ubsan_handle_mul_overflow
+
+// CHECK: [[CONT5]]:
+// CHECK: call { i64, i1 } @llvm.sadd.with.overflow.i64(
+// CHECK: br i1 %{{.*}}, label %[[CONT7:.+]], label %[[HANDLE_ADD_OVERFLOW:[a-z0-9._]+]],
+
+// CHECK: [[HANDLE_ADD_OVERFLOW]]:
+// CHECK: call void @__ubsan_handle_add_overflow
+
+// Check that the detach ends up after the loop-variable init expression.
+
+// CHECK: [[CONT7]]:
+// CHECK-NEXT: detach within %[[SYNCREG:.+]], label %[[PFOR_BODY_ENTRY:.+]], label %[[PFOR_INC:.+]] unwind label %[[LPAD9:.+]]